Field of the Invention
The present invention relates generally to a method of applying a binder composition onto a lignocellulosic substrate. Specifically, the present invention relates to a method of adjusting the tack value profile of a binder composition that is applied onto a lignocellulosic substrate.
Background Information
Lignocellulosic composite panels, such as “particleboard”, are typically manufactured by applying a binder to a plurality of particles, which are being tumbled in a rotary blender, to form a mixture. Afterwards, the mixture is subjected to a pressing stage that utilizes heat and pressure to cure the mixture and ultimately form the composite.
While urea formaldehyde (UF) based binders have typically been used in the composite panel industry, UF based binders have several shortcomings that have forced manufacturers in the industry to seek an alternative binder system. For instance, one shortcoming is the possible release of formaldehyde from the composite panel after the panel has been in service in a heated environment. Manufacturers, therefore, have attempted to use polyphenylene polymethylene polyisocyanate (PMDI) based binders in the manufacture of composite panels. While PDMI based binders do not possess many of the shortcomings associated with UF based binders, potential issues can still arise with the use of a PMDI based binder in the manufacturing process. For example, while PMDI based binders typically possess many of binding characteristics exhibited by UF based binders, PMDI based binders can exhibit lower tack values when compared to a UF based binder system. For example, the lower tack values of the binder can causes a variety of issues during the process of manufacturing particleboard since a “pre-mat” that is formed from a mixture of the PMDI based binder and a lignocellulosic material can only be used in limited circumstances during the manufacturing process. To compensate for the lower tack values, manufacturers have resorted to using tackifiers. The use of these tackifiers, however, has several shortcomings such as adding cost and complexity to the manufacture of a composite panel. For example, at times the manufacturing process would have to be stopped in order to remove “tackifier build-up” from the equipment used in the manufacturing process.